FIG. 21 shows an absorption chiller which comprises a condenser 11 and low temperature generator 12 arranged in an upper shell 1, an evaporator 21 and absorber 22 arranged in a lower shell 2, a high temperature generator 3 incorporating a burner 31, a high temperature heat exchanger 4, low temperature heat exchanger 5, etc. These components are interconnected by piping to recycle an absorbent through the high temperature generator 3, low temperature generator 12 and absorber 22 by an absorbent pump 6 and realize refrigeration cycles. Cooling water from a cooling tower (not shown) flows through cooling water piping extending through the absorber 22 and condenser 11. The supply of fuel gas to the burner 31 is adjusted to maintain at a target value the temperature of cold water to be supplied from the evaporator 21.
Foulness of the cooling water, an abnormal amount of recycling of the absorbent, abnormal vacuum, contamination of the refrigerant with the absorbent and like abnormalities are likely to occur in the absorption chiller.
When the cooling water becomes fouler, extraneous matter such as dirt adheres to the inner surface of the cooling water piping to result in a lower coefficient of heat transfer, and the condenser 11 and the absorber 22 fail to produce a sufficient cooling effect to result in impaired refrigeration capacity. If contaminated with the absorbent, the refrigerant exhibits a lower boiling point, consequently reducing the internal pressure of the lower shell 2 to lower the capacity of the evaporator 21 and the absorber 22. A reduction in the vacuum in the lower shell 2 also impairs the capacity of the evaporator 21 and the absorber 22.
It is therefore practice to monitor variations in logarithmic mean temperature differences in heat exchanger units such as evaporator 21, absorber 22 and condenser 11 in order to diagnose abnormalities in the interior of the chiller. Thermocouples, thermistors or like temperature sensors are attached to the inlet and outlet of these heat exchange units for measuring the fluid temperature at the inlet and outlet of each unit. Further the refrigerant is checked for contamination with the absorbent by drawing off the refrigerant trapped in the lower shell 2 and measuring the specific gravity of the refrigerant.
On the other hand, we have proposed a method of diagnosing failures based on an abnormality degree A defined by the following mathematical expression 1 as an index representing the degree of abnormality of heat exchange units.
Mathematical Expression 1: EQU A=(.DELTA.T-.DELTA.Tn)/.DELTA.Tn
wherein .DELTA.T is an actual logarithmic mean temperature difference (measured value) obtained by measurement, and .DELTA.Tn is an ideal logarithmic mean temperature difference (normal value).
However, the following problems are encountered with conventional absorption chillers.
(1) Calculation of the logarithmic mean temperature difference and the degree of abnormality requires 3 to 4 temperature sensors for one heat exchange unit, so that the entire main assembly of the chiller needs to be equipped with a considerable number of temperature sensors if the required sensors are to be mounted on all the heat exchange units. Moreover, the calculation of the logarithmic temperature difference requires a computer program and memory for logarithmic calculation to entail the problem of necessitating a circuit of increased scale.
(2) While the abnormality degree of the absorber 22 is an important index in detecting various abnormalities, cooling water flows through the absorber and therefore exerts a great influence if fouling. Nevertheless, even while the chiller is in continued normal operation, the foulness of the cooling water increases with the operating time, so that an increase in the abnormality degree of the absorber can not be interpreted as indicating occurrence of some abnormality other than fouling of the cooling water. Thus, in diagnosing a failure based on the abnormality degree of the absorber, it is conventionally impossible to make distinction between fouling of the cooling water and other cause, and difficulty is encountered in detecting a truly objectionable abnormality such as contamination of the refrigerant or an abnormal vacuum.
(3) If the concentration (concentrate concentration) of the absorbent (lithium bromide solution) to be supplied from the low temperature generator 12 to the absorber 22 via the low temperature heat exchanger 5 exceeds a definite value, the absorbent crystallizes to cause trouble to the operation. The conventional chiller is accordingly equipped with a safety device for monitoring the concentration of the absorbent at all times and discontinuing the operation of the chiller upon the concentration exceeding the definite value. Since measuring the concentrate concentration necessitates an expensive concentration meter, the Duhring diagram shown in FIG. 7 is usually used to estimate the concentration based on the saturated vapor temperature Tcond of the condenser 11 and the absorbent temperature Ts.sub.-- hi at the outlet of the low temperature generator 12 as actually measured.
More specifically, the concentrate concentration is determined with reference to the Duhring diagram by locating the intersection of the saturation pressure Ps of water corresponding to the saturated vapor temperature Tcond and the absorbent temperature Ts.sub.-- hi and reading the concentration Ds at the intersection. Since the saturated vapor temperature Tcond can not be determined accurately by directly measuring the temperature of the vapor flowing through the upper shell 1, the temperature Tcond is calculated from the measurement of internal pressure Pup of the upper shell 1 with reference to the Duhring diagram of FIG. 7.
However, the method of calculating the saturated vapor temperature Tcond from the internal pressure Pup of the upper shell 1 still has the problem that the pressure sensor is more expensive than the thermometer and difficult to maintain.
On the other hand, an operation monitoring system has been proposed for calculating the concentrate concentration in theoretical cycles based on the temperature measurements of various portions (Examined Japanese Patent Publication SHO 63-297970), whereas since the system operates on the premise of the theoretical cycle, the difference between the calculated concentration and the concentration in the actual chiller is great to entail the problem that it is difficult to accurately detect abnormal concentrations.